The present invention relates to an improved system for removal of debris from a fish pen.
It is common practice for the commercial purposes to grow aquatic organisms such as fish and the like in tanks or bag like structures hereinafter referred to as fish tanks or pens. One of the main problems of growing these aquatic organisms is the disposal of sediment such as excrement and other debris that would otherwise build in the bottom of the tank or to be released into the surrounding waters and cause contamination detrimental to the process or the surrounding environment.
There have been numerous proposals and applied systems for cleaning aquaculture tanks many of which take the debris off from the bottom of the tank. See for example U.S. Pat. No. 4,655,169 issued Apr. 7, 1987 to Paliola; U.S. Pat. No. 4,798,168 issued Jan. 17, 1989 to Vadseth et al.; U.S. Pat. No. 5,593,574 issued Jan. 14, 1997 to VanToever; U.S. Pat. No. 5,636,595 issued Jun. 10, 1997 to Lunde et al.; and U.S. Pat. No. 6,093,320 issued Jul. 25, 2000 to White.
All of the systems described in the patents use water movement to help to deliver the sediment to a sediment outlet, for example rotating flow in circular tanks to sweep the sediment toward the centre of the tank U.S. Pat. No. 4.655,169 referred to above describes a system wherein conical grooves are provided in the bottom end of the tank and a circular flow is imparted into the water in the tank to cause the debris that settles to the bottom of the tank to be swept along the conical grooves into a collecting chamber or sump at the center of the tank. This system obviously relies on gravity for separation of the sediment from the water i.e. the sediment falls by gravity to the bottom of the tank and thus concentrated debris is swept along the helical bottom passages to a sump.
U.S. pat. No. 4,798,169 injects fresh water substantially tangentially adjacent to the top of the tank and imparts a significant velocity to the water to cause it to flow around the tank with sufficient velocity to cause the fish in the tank to orient themselves relative to the current created by the circular flow in the tank. A simple outlet is provided at the apex of the tapered bottom of the tank and the debris is brought to this outlet for removal from the tank by the circulating water.
U.S. Pat. No. 5,593,574 discloses a water treatment system for fish tanks that includes a biofilter system that uses a spray bar to distribute water over a bed of pellets. The treated water is removed adjacent to but spaced above the bottom of the biofilter tank through an outlet pipe having an inlet sheltered under a cone. Debris is removed through a sump at the bottom of the biofilter tank surrounding the outlet pipe.
U.S. No. Pat. 5,639,595 employs an annular chamber or sump surrounding a main tank outlet defined by an upper deck spaced from the bottom of the tank to provide a flow inlet extending around the full circumference of the sump. The sump is frusta-conical tapering towards a bottom end that is provided with a debris outlet adjacent to the central or axial main outlet passage from the tank. Outlet holes connect the sump with the main outlet passage at a position well above the debris outlet in the bottom of the sump. Water carrying debris flows into the chamber substantially radial around the full periphery of the chamber and towards the bottom and then flows back up and out through the outlet passages leading to the main passage. Debris falling from the water entering the sump is removed via the debris outlet. This system does not significantly concentrate the sediment for removal.
U.S. Pat. No. 6,093,320 belonging to the same company as the present invention teaches a cleaning system that employs a baffle system and injectors for imparting tangential velocity to the water entering the sump to separate the debris below the baffle and remove it through a sump and the cleaned water that carried the debris into the sump flows over the baffle and is released.
It is an object of the present invention to provide a debris separating system that is easy to operate and employs the water currents in the fish tank to deliver the debris to an outlet. Broadly the present invention relates to a debris separating system for separating debris in a fish tank having a substantially circular cross section and wherein incoming water is pumped into the tank with momentum substantially tangent to the periphery of said tank to cause said water to flow with a circular motion from the top toward the bottom of said tank, said tank having a bottom, said debris separating system comprising a standpipe concentric with said tank and extending through said bottom of said tank to a position below a surface of water in said tank, said stand pipe having an open upper end spaced from said bottom of said tank, and expanded section of said standpipe surrounding said open end, a cover concentric with said open end and spaced above said open end to define an inlet passage into said open end between said expanded section of said standpipe, said cover having a diameter greater than said open upper end to shelter said open end from debris that may fall from water above said open end and to disrupt a vortex formed in said tank by said incoming water.
Preferably the ratio of the depth D of said open upper end of said standpipe from said surface of said water in said tank to the depth d to said bottom of said tank is between 0.7 and 0.9.
Preferably said debris separating system further comprises a plurality of circumferentially spaced vanes arranged symmetrically around said inlet passage.
Preferably, said vanes have a pair of opposite faces along which said water flows into said open end and wherein said faces are oriented at an angle of between 35 and 50xc2x0 to a radius of said standpipe.
Preferably said cover is a convex dome shape with its convex surface facing away from said open upper end.
Preferably said dome is substantially conical.
Preferably said debris separating system further comprises an inverted cone concentric with said open upper end with its conical surface facing said open end, said inverted cone having a diameter less than said diameter of said dome.
Preferably said outlet system combines with the adjacent portions of said bottom of said tank to define a transition zone surrounding said standpipe
Preferably a debris outlet is provided through said bottom wall adjacent to said standpipe.